Cooling apparatus of this type includes in particular so-called travelling grate coolers, thrust grate coolers and the like which are used in order for material which has been previously burnt in a kiln, particularly cement clinker and other mineral materials, to be drastically cooled immediately thereafter with the aid of cooling air or cooling gases. The mostly red-hot material coming out of the kiln should be both cooled and well distributed in the material inlet portion so that it can then be passed in an even distribution to the cooling grate on which the main part of the cooling is carried out while the material is being transported.
If for example, one considers the cooling of cement clinker which has previously been burnt in a mixture of different grain sizes in a rotary kiln, then care should be taken to ensure that when the hot cement clinker is discharged from the kiln into the cooling apparatus which is arranged immediately after it a separation of the essentially granular clinker takes place in such a way that a quantity of predominantly coarse material is deposited on one side of the cooler and a quantity of predominantly fine material is deposited on the other side of the cooler.
This results in the formation of layers of cooled material with differing air permeability over the breadth of the cooling apparatus. Since air always seeks the path of least resistance, the greater proportion of the quantity of cooling air introduced in the cooler inlet portion or the material transfer arrangement thereof will flow through the coarse material and only a small proportion of the cooling air which has been introduced will flow through the fine material, so that cooling of the latter at least in the material inlet portion of the cooling apparatus is quite unsatisfactory or even does not occur at all in places. Attention should also be paid to the fact that in cooling apparatus with cooling grates, particularly in the case of so-called thrust grate coolers but also to some extent in the case of so-called travelling grate coolers, there is a danger of a so-called "mushroom formation" (mushroon-like buildup or growth of hot material on the material transfer surface) in the inlet portion.
Attempts have already been made to reduce this mushroom formation by having the upper surface of the material transfer arrangement which comes into contact with the material constructed with water-cooled plates, but this has the disadvantage that it reduces the required degree of recovery. Another proposal which has already been made is to provide the material transfer arrangement of the material inlet portion with an aerating base in which the flow resistance for the cooling air is greater than in the cooled material embankment: however, even this only has the effect of somewhat reducing the aforesaid problems.
Furthermore, it is also already known to use mechanical discharge means which can be moved to and fro in order, in particular, to remove larger lumps of material as quickly as possible from the impact region of the material transfer arrangement in order to reduce the danger of mushroom formation. Here too, however, it has been shown that the distribution of cooling air is still most unsatisfactory and even when the cooling air is introduced in pulses the occurrence of so-called "red rivers", i.e. essentially red-hot uncooled streams of material, must be expected.